/*******************************************************************************
 * Copyright 2014 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.jzy.game.ai.fsm;

import java.util.ArrayList;
import java.util.List;

/**
 * 堆栈式状态机，可依次返回之前状态 ，如菜单列表
 * <br>
 * A {@link StateMachine} implementation that keeps track of
 * all previous {@link State}s via a stack. This makes sense for example in case
 * of a hierarchical menu structure where each menu screen is one state and one
 * wants to navigate back to the main menu anytime, via
 * {@link #revertToPreviousState()}.
 * 
 * @param <E>
 *            the type of the entity owning this state machine
 * @param <S>
 *            the type of the states of this state machine
 * 
 * @author Daniel Holderbaum
 * 
 * @fix JiangZhiYong
 */
public class StackStateMachine<E, S extends State<E>> extends DefaultStateMachine<E, S> {

	private List<S> stateStack;

	/**
	 * Creates a {@code StackStateMachine} with no owner, initial state and global
	 * state.
	 */
	public StackStateMachine() {
		this(null, null, null);
	}

	/**
	 * Creates a {@code StackStateMachine} for the specified owner.
	 * 
	 * @param owner
	 *            the owner of the state machine
	 */
	public StackStateMachine(E owner) {
		this(owner, null, null);
	}

	/**
	 * Creates a {@code StackStateMachine} for the specified owner and initial
	 * state.
	 * 
	 * @param owner
	 *            the owner of the state machine
	 * @param initialState
	 *            the initial state
	 */
	public StackStateMachine(E owner, S initialState) {
		this(owner, initialState, null);
	}

	/**
	 * Creates a {@code StackStateMachine} for the specified owner, initial state
	 * and global state.
	 * 
	 * @param owner
	 *            the owner of the state machine
	 * @param initialState
	 *            the initial state
	 * @param globalState
	 *            the global state
	 */
	public StackStateMachine(E owner, S initialState, S globalState) {
		super(owner, initialState, globalState);
	}

	@Override
	public void setInitialState(S state) {
		if (stateStack == null) {
			stateStack = new ArrayList<S>();
		}

		this.stateStack.clear();
		this.currentState = state;
	}

	@Override
	public S getCurrentState() {
		return currentState;
	}

	/**
	 * Returns the last state of this state machine. That is the high-most state on
	 * the internal stack of previous states.
	 */
	@Override
	public S getPreviousState() {
		if (stateStack.size() == 0) {
			return null;
		} else {
			return stateStack.get(stateStack.size() - 1);
		}
	}

	@Override
	public void changeState(S newState) {
		changeState(newState, true);
	}

	/**
	 * Changes the Change state back to the previous state. That is the high-most
	 * state on the internal stack of previous states.
	 * 
	 * @return {@code True} in case there was a previous state that we were able to
	 *         revert to. In case there is no previous state, no state change occurs
	 *         and {@code false} will be returned.
	 */
	@Override
	public boolean revertToPreviousState() {
		if (stateStack.size() == 0) {
			return false;
		}

		S previousState = stateStack.remove(stateStack.size() - 1);
		changeState(previousState, false);
		return true;
	}

	private void changeState(S newState, boolean pushCurrentStateToStack) {
		if (pushCurrentStateToStack && currentState != null) {
			stateStack.add(currentState);
		}

		// Call the exit method of the existing state
		if (currentState != null)
			currentState.exit(owner);

		// Change state to the new state
		currentState = newState;

		// Call the entry method of the new state
		currentState.enter(owner);
	}

}
